1. Technical Field
The invention relates to active noise reduction and more particularly to suppression of low frequency spill over in a wide field, live performance type venue, through destructive interference of the spillover.
2. Description of the Problem
High fidelity sound systems for large auditorium and free field applications are readily made directional in the middle and upper frequencies. This helps direct sound energy toward the intended audience. However, most loudspeaker units perform increasingly as omnidirectional or monopole devices as the sound frequency reproduced decreases. This relatively difficult to direct low frequency, long wavelength sound energy can spill over into undesired areas, such as a stage set up in the field of view of the audience and on which an open microphone may be located. Where an open microphone is present spillover can lead to feedback, limiting the allowable gain from the microphone. On stage performers can find the spillover low frequency noise a distraction and highly misleading as to the character of the sound in the intended area of coverage.
Active sound cancellation is a developing field using destructive interference to produce a null sound field. The selective cancellation of low frequency sound would be made easier by availability of a directed beam low frequency device capable of relatively high levels of power output.